The present invention relates to an ignition device for a motor vehicle engine and, more particularly, to a ignition signal sampling device for detecting and observing the ignition spark voltage signals produced by the ignition system.
An ignition device for a motor vehicle engine is known having at least one ignition coil and a secondary side testing or signal sampling device for detecting the ignition voltage signals. An ignition device of this type has been described in U.S. Pat. No. 3,959,725 and German Published Patent Application 37 05 692.
The capacitive pick-up of the ignition voltage signals from the ignition coil in the ignition coil assembly is performed with the help of differently adapted sensor or adapter plates in the known devices for secondary side ignition signal sampling or signal detection. That means that the capacitive adjustment is made possible by special adjustment of sensor plates to the shape of the coil assembly. Similarly, an ignition coil signal sampling device described in German Published Patent Application 37 05 692 has a cable containing a conductor mounted on the outer surface of the housing of the ignition distributor with the ignition coil in it for read out of the ignition energy of the transmitted signal. This method and the other prior art methods however lead to difficulty, because the measured signal which they produce is influenced by events in the primary circuit of the ignition coil as well as the secondary coil voltage built up. Moreover, for each ignition spark event the transmitted signals must be such that equal-sized signals are produced for the same ignition voltage in the ideal ignition signal sampling device.
Similarly, the adjustment possible in rotating high voltage distributors at the spark cable is often not possible in the ignition system with stationary high voltage distribution and/or individual spark generation, since a direct access to the secondary side of the ignition coil is not possible, for example by a diode in the secondary circuit or a direct connection between the secondary coil and the spark plug without rebuilding or redesign of the unit.